Project Summary/Abstract Depression among adolescents is a major concern in the United States (U.S.). It is estimated that the prevalence of depression among those 12 to 17 years old was 12.5% or 3 million in 2015.5 This represents a serious public health issue as adolescents who are depressed have an increased risk of comorbid psychiatric disorders, suicide, and substance abuse compared to adolescents who are not depressed. Few studies have examined the role of neighborhoods on depression, especially among adolescents. To address this gap, this secondary data analysis study of a representative sample of U.S. adolescents proposes to (1) determine the association between adolescent-perceived collective efficacy and depressive symptoms among U.S. adolescents at baseline, (2) examine the moderating role of adolescent-perceived collective efficacy and parental-perceived collective efficacy on the association between neighborhood structural disadvantage and levels of depressive symptoms among U.S. adolescents at baseline, separately, and (3) estimate the change trajectories in the relationship between depressive symptoms and in neighborhood structural disadvantage among U.S. adolescents at baseline, one year later, and eight years later. The central hypothesis is that neighborhood structural disadvantage and collective efficacy will affect depressive symptoms among adolescents, partially explaining the increase in depression among U.S. adolescents. The proposed study will use 8 years of data from the National Longitudinal Study of Adolescent to Adult Health (Add Health), a longitudinal study comprised of U.S. adolescents in grades 7?12. The total sample size is 24,210 with adolescents and their parents representing various racial/ethnic groups. Multilevel modeling will be used to determine the effect of neighborhood structural disadvantage and collective efficacy on depressive symptoms. The findings from the proposed study would help in the identification of neighborhood characteristics that impact depressive symptoms and subsequently depression incidence among adolescents in the U.S. Components of neighborhood structural disadvantage and collective efficacy would serve as targets for the development of structural and other intervention strategies such as community-level interventions, aimed at reducing or preventing depression. Ultimately, addressing neighborhood structural disadvantage and improving collective efficacy may help to reduce depressive symptoms and increase mental health utilization among adolescents, thereby reducing the growing mental health burden among youth.